what open does
open adds a tail that follows your source: louder bands can decay sooner or longer depending on bloom, so the reverb sits around the part instead of washing over it.
under the hood it measures the input across frequency bands and maps those readings to decay times. focus sets how much that map moves with the music; bloom sets whether strong bands get shorter or longer tails.
what open is not for
- i would not choose open to reproduce a particular sampled room or hardware plate.
- i would not use it to remove room sound already recorded into a source.
- i would not expect reverse to create a swell before an incoming live note.
- i would not expect length to guarantee one identical decay time across every frequency and character.
quick start
first time? start here
- insert open on a track or return and play your material
- load preset init, then pick hall or room
- set depth around 25–40% to start
- toggle delta to hear only the wet tail, then turn delta off and adjust depth
- hit bypass to compare dry vs processed
an insert
- put open on the source and choose init from the preset menu.
- try room, hall and cloud, then set length so the tail ends where the phrase wants it to.
- turn depth up until the tail sits behind the part, then flip bypass to compare.
a shared return
- put open on a return and set depth to 100%.
- send your tracks to it and balance them with their send levels.
- if the tail gets in the way, select sidechain wet so the source ducks it. you can also route a key from another track, a kick for example.
a frozen tail
- play a note or chord until there is a tail you like.
- tap freeze to hold it, or keep the button pressed to hold it only while you press.
- tap again (or let go) to release it. if length is turned all the way up, turn it down too, since the top of length is also freeze.
listen
hear the difference.
matched-level A/B clips from the same sources as the product page. switch variants while it plays.
🎧 for best results, listen on headphones or studio monitors.
a pad in HALL. with FOCUS up, louder bands steer the tail more. at 0 the decay map stays flat.
space: play/pause. left/right or a/b: switch.
loading audio
a pad in HALL, TONE at −6 and +6 dB. tone shelves the wet path only. the dry stays unchanged.
space: play/pause. left/right or a/b: switch.
loading audio
a pad in HALL, same depth and length. low bloom shortens loud bands; high bloom lets them ring.
space: play/pause. left/right or a/b: switch.
loading audio
controls
these are parameter defaults. loading a preset can change them. the tail eq has four editable bands.
| control | range | default | what it does | what you hear |
|---|---|---|---|---|
| depth | 0 to 100% | 30% | blends dry input with reverb using an equal-power curve. at 100%, the dry contribution is removed. | turn left: more dry in the blend. turn right: more reverb and less direct signal. |
| length | 0.1 to 12 s | 1.8 s | sets the decay-time reference. actual decay varies by frequency and character. at 11.95 s and above, it enters freeze. | turn left: shorter decay. turn right: longer tail; near max the tail can latch in freeze. |
| focus | 0 to 100% | 40% | sets how strongly the source spectrum changes decay times. bloom determines whether stronger bands decay sooner or later. | turn left: decay times stay closer to flat. turn right: louder bands steer the tail more. |
| bloom | 0 to 100% | 60% | shortens stronger bands below 50% and extends them above 50%. at 50%, focus has no effect on the decay-time mapping. | turn left: strong bands decay sooner. turn right: strong bands ring longer; at 50% focus has no spectral map. |
| tone | -6 to +6 db | 0 db | applies opposing low and high shelves to the reverb. the dry signal is unchanged. | turn left: darker wet tone. turn right: brighter wet tone; dry stays unchanged. |
| character | room / hall / cloud | hall | selects delay, diffusion and decay settings. room and hall add early reflections. cloud omits those reflections and spreads incoming excitation over one second. | room: shorter space. hall: longer hall tail. cloud: smeared bed without early reflections. |
| m/s | off / on | off | encodes the wet processing input as mid and side, then decodes it before mixing with dry. source analysis uses the mid signal. | off: normal stereo wet path. on: encode/decode mid-side; analysis listens to mid. |
| delta | off / on | off | isolates the wet signal at the current depth, with auto comp bypassed. it does not subtract the dry waveform from the reverb. | off: normal depth blend. on: wet only at the current depth setting. |
| auto comp | off / on | on | adjusts wet gain against dry loudness, holding gain during freeze and reverse. delta bypasses it. cloud applies no compensation even when the button is on. | off: no loudness match on the wet path. on: wet level tracks dry loudness (bypassed in delta, off in cloud, held during freeze and reverse). |
| sidechain enable | off / on | off | enables ducking from an external sidechain when connected, otherwise from the dry input. the key reduces level; spectral analysis keeps listening to the main input. | off: no ducking. on: key lowers level when the source or external key is loud. |
| sidechain target | wet / all | wet | wet ducks the reverb. all ducks the mixed output including dry. the sidechain button cycles off, wet and all. | wet: only the reverb ducks. all: the whole output ducks including dry. |
| reverse | off / on | off | plays overlapping sections of the wet tail backwards. length sets the reversal window, limited to 0.4 to 2 seconds. | off: forward tail. on: slices of the tail play backward. |
| freeze | off / on | off | holds the existing late tail and stops new input entering the loop. tap toggles the latch. hold longer than 300 ms from off for momentary freeze. double-clicking length toggles the latch without moving length. | off: decay runs normally. on: holds the late tail; new input stops feeding the loop. |
| bypass | off / on | off | bypasses reverb processing. i use it to compare the input with the processed result. | off: processed output. on: dry input only. |
| range low | 20 to 2,000 hz | 20 hz | removes low frequencies from the signal feeding the late tail. at 20 hz this filter is bypassed. | turn left (toward 20 hz): more lows feed the tail. turn right: lows are cut from the excitation. |
| range high | 500 to 20,000 hz | 20,000 hz | removes high frequencies from the signal feeding the late tail. at 20,000 hz this filter is bypassed. | turn left: highs are cut from the tail feed. turn right (toward 20 khz): full bandwidth. |
| tail eq frequency | 20 to 20,000 hz | 80 / 500 / 3,000 / 10,000 hz | positions each of the four wet-output eq bands. these controls shape the reverb after the late loop. | drag left/right: move the band in the spectrum. |
| tail eq gain | -12 to +12 db | 0 db | boosts or cuts the selected wet frequency region. the dry signal is unchanged. | turn down: less level in that wet band. turn up: more level in that wet band. |
| tail eq width | 0.3 to 6 | 1 | changes each band's width. higher values make bell bands narrower. | turn left: wider band. turn right: narrower band. |
| tail eq enable | off / on | off | enables the individual band. disabled bands do not apply their eq settings. | off: band inactive. on: band shapes the wet output. |
| tail eq routing | stereo / mid / side / left / right | stereo | selects the component processed by that band. each band has its own routing choice. | pick which component (stereo, mid, side, left, or right) the band processes. |
| tail eq shape | bell / shelf | bell | switches the lowest or highest node between bell and shelf. the two middle nodes remain bells. | outer bands: switch between bell and shelf shape. |
characters
room, hall and cloud change the delay, diffusion and decay settings. i compare them on the same source before adjusting length.
room
room combines early reflections with a late tail. the early reflections keep the source's direction, while the late loop receives the mid signal.
hall
hall uses its own early-reflection pattern and late-tail settings. it also keeps the early reflections separate from the mid-fed late loop.
cloud
cloud omits the early-reflection contribution and spreads input to the late loop over one second. auto comp stays at unity, so it does not adjust the wet gain.
spectral display
frequency runs horizontally. the spectrum shows signal level by frequency. normally it shows the dry input; with delta on, it shows the wet signal with the dry spectrum behind it.
the decay curve shows decay-time targets relative to length. i read that separately from the spectrum level and the editable tail eq curve.
i drag the tail eq nodes to change frequency and gain, and use the mouse wheel over a node to change its width. the edge handles set the frequency range feeding the late tail.
reading the display
the spectral display shows +12 dB to -60 dB. a curve flat along the top line is above the display range, not clipping in the audio. the display clamps the visualization at +12 dB to fit loud peaks within the window. the audio itself is not clipped. if the trace rides the top edge on a loud passage, turn down the send or depth before you chase eq.
presets
i use presets as starting points, then adjust depth for the source. click the preset name to open the menu, or use the arrows to browse.
the menu groups presets by room, hall and cloud. choose init to return to the parameter defaults listed above.
tips
hear the breathing tail
set focus to 0 and listen for the note and tail fighting for space. raise focus toward 70% and pull bloom left: the center opens and the tail wraps the phrase instead of masking it. that push-and-release is what i mean by breathing. fine-tune depth and bloom from there.
gain staging
open runs in 32-bit float, so the wet path does not clip internally at the bus. level still matters: more input excites the FDN and early reflections harder, and with sidechain ducking enabled the key envelope maps input amplitude to wet gain. a quiet dry leaves more tail; a loud phrase ducks the wet toward ~-9 dB. auto comp on the output matches K-weighted loudness to the dry; it is not a peak limiter. i gain-stage the send or insert so the tail sits in the mix, then use depth and ducking for phrase shape.
auto comp measures K-weighted loudness of the input and output, then applies makeup gain to match them. it does not process or remove noise. if the source has noise and open adds reverb, auto comp will raise the gain to match the input loudness, which also raises the noise. i turn auto comp off when comparing a noisy source, or i accept that the output will match the input loudness, noise included. cloud holds auto comp at unity, so it does not apply any makeup gain.
where in the chain
i start with an insert when one source needs its own space, adjusting depth to blend it. on a shared return, i set depth to 100% and use send levels to balance the sources.
i use a post-fader send when reverb should follow the source fader, or pre-fader when i want independent feeding of the return. i put corrective processing before open to change what excites the tail; processing after open shapes its output.
i leave headroom and check the return after boosting tone or eq. auto comp is not a peak limiter, and cloud does not apply automatic gain compensation.
i also listen to the return in mono before settling on its level.
troubleshooting
| what i hear | what i check |
|---|---|
| silence in delta | i raise depth. delta follows the wet level, so depth at 0% is silent. i also check that there is input or an existing tail. |
| the tail keeps holding | i turn freeze off and bring length below 11.95 s. either control can hold the tail. |
| sidechain seems inactive | i cycle the sidechain button to wet or all. for an external key, i check the host routing. without an external connection, it uses the dry input. |
| the dry signal ducks too | i switch the sidechain target from all to wet. |
| auto has no effect in cloud | cloud holds compensation at unity even when auto is on. i set the output balance with depth and the track or return level. |
| focus seems inactive | i check bloom. at 50%, focus does not change the decay-time mapping. |
| open does not appear in the host | i check the installation paths above, then rescan plugins. |
keyboard / mouse reference
| action | control |
|---|---|
| adjust a knob | click and drag |
| fine-adjust depth, length, focus or tone | shift + drag |
| latch or release freeze | tap freeze, or double-click length |
| momentary freeze from off | hold freeze longer than 300 ms, then release |
| change tail eq frequency and gain | drag a node horizontally and vertically |
| change tail eq width | mouse wheel over a node |
| fine-adjust tail eq | shift + drag a node |
| enable or disable a tail eq band | double-click its node |
| type tail eq values | double-click its label |
| choose tail eq routing | right-click its node |
| change an outer band's shape | click its type badge |
| change the range feeding the tail | drag a spectrum edge handle |
| reset a range cutoff | double-click its edge handle |
| browse presets | click the header arrows |
| open the preset menu | click the preset name |
for the curious
deeper signal-path detail, specs and install paths. skip this on a first pass.
latency
open reports 256 samples of latency, about 5.8 ms at 44.1 khz. there is no live button.
i check the host's plugin delay compensation setting when placing open in a session. reverse's delayed swells are part of the effect; turning it on does not change the reported latency.
how it works
- listen. the input is split into bands so focus and bloom know which frequencies are loud. source: PluginProcessor.cpp:641-659.
- space. room and hall add early reflections; cloud smears excitation for about one second before the late loop. source: dsp/OpenConstants.h:126; docs/dsp/open-algorithm.md:1320.
- tail. a feedback delay network carries energy until the decay map fades it by band. length sets the time reference. source: docs/dsp/open-algorithm.md:484-529.
- polish. tone and tail eq shape the wet path; depth blends wet and dry; sidechain and auto comp trim level. source: dsp/OpenOutputStage.cpp:149-170; PluginProcessor.cpp:1165-1185.
specifications
| specification | detail |
|---|---|
| cpu | about 3% on macOS at 44.1 kHz, single instance (ROOM about 2.4%, HALL and CLOUD about 3%) |
| formats | VST3, AU (macOS), AAX, standalone |
| platforms | macos + windows |
| mac requirements | macos 10.13+ (intel) or 11+ (apple silicon) |
| windows requirements | windows 10+, 64-bit |
| license | lifetime license. no ilok, no account, no subscription. offline use. |
installation
get open from the product page.
macos
- copy
KERN OPEN.vst3to~/Library/Audio/Plug-Ins/VST3/. - for au, copy
KERN OPEN.componentto~/Library/Audio/Plug-Ins/Components/. - for aax, copy
KERN OPEN.aaxpluginto/Library/Application Support/Avid/Audio/Plug-Ins/. - rescan plugins in the host. look for
KERN OPENunderKERN Audio.
windows
- copy
KERN OPEN.vst3toC:\Program Files\Common Files\VST3\. - copy
KERN OPEN.aaxplugintoC:\Program Files\Common Files\Avid\Audio\Plug-Ins\. - rescan plugins in the host. look for
KERN OPENunderKERN Audio.
version history
v1.1.0 (september 25, 2026)
now available as aax for pro tools on macos and windows. a small lock next to depth keeps your depth setting when you switch presets, handy on a return bus. auto is greyed out in cloud, where cloud already holds the level. hold shift while using the mouse wheel on a knob for fine steps. the frequency labels on the display are easier to read.
v1.0.0 (september 2026)
initial release. room, hall and cloud, with tail eq, freeze, reverse and sidechain ducking. the late loop receives the mid signal. cloud spreads incoming excitation and holds auto comp at unity.